骨料级配对混合骨料混凝土性能的影响

采用了三种不同级配的普通骨料与轻骨料混合配制混凝土,通过测定其分层度、强度、弹性模量、早期收缩裂缝、氯离子扩散系数和冻融情况,系统研究了骨料级配对混合骨料混凝土宏观性能的影响规律,再辅以界面区孔结构的测定进一步证实了耐久性影响机理。结果表明,小粒径陶粒与大粒径碎石的混合级配有利于混凝土力学性能的提高,同时小粒径陶粒由于较大的比表面积使得其在混凝土内部的返水作用也更显著,可细化界面区水泥石的孔结构,进而改善混凝土早期收缩开裂以及后期抗渗和抗冻性,但较大粒径的碎石会加剧混合骨料混凝土的分层现象,应适当加以控制。     

骨料对混凝土工程耐久性的影响

本文主要阐述了骨料对建筑工程安全性和耐久性的影响。     

钢-无机纤维对轻骨料混凝土力学性能及耐久性能的影响

为了研究钢-无机纤维对轻骨料混凝土力学性能和耐久性能的影响,设计不同掺量的单掺陶瓷纤维和玄武岩纤维以及不同掺杂方式的混杂钢-玄武岩纤维和钢-陶瓷纤维增强轻骨料混凝土试件。结果表明,钢-玄武岩纤维对轻骨料混凝土抗压强度和60d透水时水压强度提高最明显,最大增幅分别达14.5%、42.9%;掺入1.35kg/m3玄武岩纤维对抗折强度增幅为62.2%;掺入陶瓷纤维降低了抗压强度和抗渗性能,但提高了抗折强度及抗冻性能;钢-陶瓷纤维对抗渗性能和抗冻性能提升效果较好。     

天然和人工骨料水工混凝土的配制及性能研究

分别选择天然砂砾石、花岗岩人工骨料开展了C30、C20水工混凝土配合比设计及性能试验,研究了骨料品种对相同强度等级混凝土拌和物性能、力学性能、绝热温升、耐久性能等方面的影响。结果表明：采用天然骨料或人工骨料,以绝对体积法设计、制备的C20W6F300、C30W6F350混凝土的强度、抗渗等级、抗冻等级均能满足设计指标要求;当强度等级相同时,两种骨料制备的混凝土拌和物性能相近,人工骨料混凝土的力学性能、抗裂性、抗冻性均优于天然骨料混凝土,但天然骨料混凝土的渗水高度小于人工骨料混凝土,C20人工骨料混凝土的绝热温升值略高于天然骨料混凝土,但两者的平均温升值相近。     

化学强化对再生骨料及再生混凝土性能的影响研究

再生骨料性能一般低于天然骨料，针对再生骨料吸水率高、强度低等问题，通过化学浆液强化方式对其进行强化，探讨对再生骨料性能、再生混凝土的力学性能和耐久性的影响。研究表明，经化学浆液强化后，再生骨料的压碎指标和吸水率明显降低，再生混凝土的力学性能和耐久性显著提升。     

人工骨料在混凝土中的应用研究

为了充分利用尾矿资源，促进天津地区人工骨料的应用，针对蓟县尾矿资源的开发利用进行了初步研究，内容包括不同种类骨料的性能及其混凝土的立方体抗压强度和抗冻性试验，实验结果表明，利用尾矿资源生产的人工骨料可以满足工程需要。     

再生骨料混凝土基本性能试验研究

对普通混凝土、石屑特细砂混凝土和再生骨料混凝土分别进行了基本性能试验研究,包括塑性混凝土性能、硬化混凝土力学性能和耐久性。试验结果表明,石屑特细砂混凝土和再生骨料混凝土具有较好的力学性能和耐久性,但碎屑特细砂混凝土的收缩值相对较大。     

骨料粒径对自密实混凝土性能的影响

文章说明了自密实混凝土性能试验的试验方法及材料,分析了结果,包括:同试验阶段不同骨料粒径区间对抗压强度、抗折强度和抗折比的影响;抗压强度与抗折强度的线性关系。     

再生骨料强化及再生混凝土性能研究

为了改善废弃混凝土骨料压碎值和吸水率较高的问题,采用水玻璃和硅烷偶联剂对废弃混凝土骨料进行化学强化,研究了强化前后压碎值和吸水率的变化规律,通过SEM电镜扫描得到强化前后的骨料表面形貌,明确了强化原因,同时将强化废弃混凝土全部代替天然骨料配制混凝土试件,分析了废弃混凝土骨料经强化后再生混凝土的力学性能和耐久性的变化规律。试验结果表明：经过强化后的废弃混凝土骨料吸水率和压碎值均得到明显改善,且提高了再生混凝土性能,降低了混凝土的孔隙率使其更加密实。水玻璃的强化效果优于硅烷偶联剂,水玻璃强化浓度宜大于20%,硅烷偶联剂掺入量宜大于4%。     

再生骨料混凝土的工程应用现状和基本性能分析

本文分析国内外再生混凝土在工程中的应用现状,通过对再生混凝土研究的进展和成果进行分析,总结了再生骨料混凝土基本力学性能、耐久性、工作性的特点,并提出了改善这些性能的方法。     

Strength and durability of concrete incorporating crushed limestone sand

In recent years, there is a growing interest in the use of crushed sand obtained from limestone quarries in some countries where river sand is not widely available. The fines content is usually high in crushed sand which can adversely affect concrete properties. The influence of fines in crushed sand on physical and mechanical properties of concrete has been widely investigated. The results proved that up to 15% of fines content in crushed sand could be used without adversely affecting concrete strength. However, little work has been done so far on the effect of fines in crushed sand on the durability of concrete. This paper examines the influence of limestone fines in crushed sand on concrete properties. Properties include strength, water, gas and chloride-ion permeability and capillary water absorption. Four different cement types were used while maintaining a constant water/cement ratio. The results show that concrete containing 15% of limestone fines as replacement of crushed sand reduces the water permeability and increases the gas and chloride-ion permeability.     

Effects of long-term magnesium sulfate crystallisation tests on abrasion and durability of andesite aggregates

Bulletin of Engineering Geology and the Environment - The durability of aggregates against salt weathering is calculated after five cycles of immersion in a magnesium sulfate solution...     

Identification of frost-susceptible recycled concrete aggregates for durability of concrete

Demolished concretes to be recycled show great diversity in property with regard to residual potential of resistance to the environmental effects such as frost action, when they are used in a new concrete as aggregate. There seems to exist no appropriate test method fitting specific characteristics of the recycled concrete aggregates with respect to the fair judgement of their unbound state frost durability. This fact rises another important prejudice against performance of recycled concrete aggregates compared to virgin alternatives. This study deals with reliable identification of frost susceptibility of recycled concrete aggregates. An unbound frost durability test with a mild pre-drying procedure (at 50 °C) was performed on recycled concrete aggregates originated from both air-entrained and non-air-entrained type of source concretes. The procedure distinctly identified the non-durable recycled coarse aggregates in parallel to freezing and thawing durability results of the concretes incorporating identical aggregates. Sulfate soundness test gave misleading results in judgement of the unbound state frost durability due to the highly disruptive physicochemical effect of the method on the recycled concrete aggregates, regardless of the air void characteristics of the materials.     

Effects of crushed clay brick aggregate on mortar durability

This paper reports an experimental study that aimed to investigate the effects of recycled clay brick, used as a part of fine aggregate, on mortar durability. The brick, in crushed form, was from a local brick manufacturer that salvages its off-standard products. It was used to replace 10% and 20% (by weight) of the river sand in mortar. Effects of the brick replacement on the mortar flow, compressive strength, shrinkage, freeze–thaw resistance, and alkali–silica reaction potential were investigated. The results showed that as the brick replacement level increased, the mortar flowability reduced. The 10% and 20% brick replacements had no negative effect on the mortar compressive strength and very limited effect on the mortar shrinkage. The freeze–thaw resistance of the mortar was improved by the brick replacement. However, the use of crushed brick as aggregate appeared not to reduce potential alkali–silica reaction. The microscopy study revealed the alkali–silica reaction product and associated cracking in the mortar. Additional study indicated that the brick aggregate used in the study had pessimum proportion, 30%, for the alkali–silica reaction expansion.     

Effect of crushed ceramic and basaltic pumice as fine aggregates on concrete mortars properties

This study examines the suitability of ceramic industrial wastes and huge amounts of basaltic pumice as a possible substitute for conventional crushed fine aggregates. Experiments were carried out to determine abrasion resistance, chloride penetration depths and the compressive strengths of concrete with crushed ceramic waste and basaltic pumice fine aggregates and to compare them with those of conventional concretes. Test results indicated that ceramic wastes and basaltic pumice concretes had good workability. Furthermore, it was found that abrasion resistance of crushed ceramic (CC) and crushed basaltic pumice (CBP) concretes was lower than that of conventional concretes. Test results also showed that maximum abrasion rate was obtained from specimen control (Mo), while minimum abrasion rate is obtained from M3 (60% crushed ceramic concrete) specimens. Abrasion resistance was increased as the rate of fine CC was decreased. Abrasion resistance of concrete was strongly influenced by its compressive strengths and CC and crushed CBP content. The crushed ceramic addition percentage decreased as the chloride penetration depth increased. Results of this investigation showed that CC and CBP could be conveniently used for low abrasion and higher compressive strength concretes.     

氯盐和硫酸盐环境下混凝土耐久性研究综述

对混凝土结构在侵蚀性环境下的长期安全服役要求使得针对混凝土材料的耐久性研究获得了越来越广泛的关注。盐环境普遍存在于大自然中,其中氯盐和硫酸盐会对混凝土结构的耐久性产生不利影响。介绍了氯盐或硫酸盐单一侵蚀因素作用下混凝土材料耐久性的研究现状,系统总结了试验方法、宏观性能和侵蚀模型等方面的研究成果,阐述了盐环境下混凝土耐久性的研究趋势。得到以下初步结论：（1）试验方法方面,由于自由扩散法控制附加因素的介入,对离子传输机理的影响较小,与实际状态更为接近;（2）基于Fick第二定律建立氯离子扩散模型,关键在于对氯离子扩散系数的修正,不同因素对扩散系数的影响应有更多基础理论和试验数据作为支撑。细观模型方面,在骨料特征的参数化技术方面寻求突破对于其仿真效果至关重要;（3）由于影响硫酸盐侵蚀的因素较多且系统性试验较少,因此已有模型的适用性存在局限,应寻求突破建立全面涵盖各类因素的模型;（4）建立自然盐环境与试验室盐环境的对应关系、保证混凝土的试验室状态与其实际服役状态的一致性以及建立特定环境下混凝土耐久性损伤的时变模型对服务工程应用具有重要意义。     

高性能混凝土耐久性能试验研究

以3种不同水胶比和矿物掺合料掺量为变量,研究混凝土抗氯离子扩散、抗渗、抗碳化性能的变化。通过试验得出:水胶比0.33,双掺(20%石灰石粉+10%矿渣)的28 d强度最高,其扩散系数最小;良好养护的混凝土试件,其材料自身的抗水渗透能力均较好,且随着强度的提高,其渗水高度略有降低。随着碳化时间的增长,混凝土碳化深度逐渐增加,但碳化28 d后平均碳化深度均小于10 mm;根据试验结果,可为今后高性能混凝土配合比设计提供依据。     

高性能轻混凝土的耐久性研究

以 陶粒 为 部分 粗集 料,并采 用掺 合 矿渣 、粉 煤灰 部分 取代 工 程砂 配制 高 性能 轻混 凝土 。对 该种 混凝 土 与其 它几种 不 同 配 比 混 凝 土 进 行 抗 渗 性 能 比 较 和 抗 冻 实 验 研 究 ,并 模 拟 海 水 进 行 混 凝 土 耐 蚀 性 实 验 研 究 与 耐 蚀 机 理 分 析 ,拟 探 索混 凝 土 相 应 的 耐 久 性 能 。     

高性能混凝土耐久性性能检测

高性能混凝土是以耐久性作为设计的主要指标,针对不同用途要求,对下列性能重点予以保证:耐久性、工作性、适用性、强度、体积稳定性和经济性。由于混凝土的冻融破坏、钢筋锈蚀、碱骨料反应都是以水渗透为前提的,因此抗渗性能是高性能混凝土最重要的耐久性能。在进行抗渗性能检测时,受仪器设备、操作手法、包裹材料等因素的影响,极易造成试验结果的不准确。本文主要论述了高性能混凝土抗渗性能检测的心得体会。     

氨基磺酸盐高效减水剂对混凝土耐久性的影响

通过混凝土试验,介绍了氨基磺酸盐高效减水剂ASH-JD对混凝土耐久性的影响.结果表明,ASH-JD掺入0.45%时,使混凝土拌合物的含气量由1.2%增加到2.3%;冻融后,混凝土的质量、强度损失率分别由2.5%,8.8%下降到1.2%,3.1%,提高了硬化混凝土的抗冻性能;透水高度由34.7 mm降到21.5 mm,透水高度比为62%,提高了硬化混凝土的抗渗性能;对收缩性能无不良影响.